MQ-3 Alcohol Meter for Flipper Zero

Breathalyzer application for Flipper Zero using MQ-3 alcohol sensor with automatic zero calibration and intoxication level detection.

Features

• Automatic Zero Calibration - Self-calibrates during warmup, adapts to any MQ-3 sensor
• 5-Level Intoxication Scale - Sober, Light, Medium, Heavy, Critical
• Peak Detection - Captures maximum value during measurement
• Sober Time Estimation - Approximate time until fully sober
• Measurement Log - Saves results to SD card with date/time
• Log Viewer - Browse measurement history with scrolling
• Heater Management - Auto-shutdown after 60s idle
• Voltage Filtering - Ring buffer + EMA smoothing for stable readings
• Vibration Alerts - Tactile feedback for each intoxication level

Hardware Connection

MQ-3 Module	Flipper Zero GPIO
VCC (5V)	Pin 1 (OTG 5V)
GND	Pin 8 (GND)
AOUT	Pin 4 (PC3/ADC)
HEATER	Pin 2 (PA7)

Important: Module includes 10kΩ + 9kΩ trimmer voltage divider. AOUT signal must not exceed 2.048V.

Installation

1. Download the .fap file from Releases
2. Copy to apps/GPIO/ on your Flipper Zero SD card using qFlipper . Launch from Apps → GPIO → MQ-3 Alcometer

Usage

Controls

Button	Action
OK	Start warmup / Begin measurement / New test
BACK	Return to main screen / Exit
LEFT	View measurement log (from main or result screen)
UP/DOWN	Scroll log entries

Workflow

1. Press OK to start sensor warmup (30 seconds)
2. Wait for warmup to complete (progress bar fills)
3. Press OK to begin 10-second measurement
4. Blow into the sensor during measurement
5. View result with peak concentration and sober time
6. Press OK for new measurement or BACK to exit

Log Viewer

• Access from main screen or result screen with LEFT button
• Scroll with UP/DOWN buttons
• Clear log with OK button (confirmation required)
• Log format: DD.MM.YY HH:MM - X.XXX mg/l
• File location: /ext/apps_data/alcohol_sensor/measuring.log

Technical Details

Calibration

Zero calibration (Z) occurs during the last 5 seconds of warmup using Exponential Moving Average (EMA): Z = α × V_new + (1 - α) × Z_old α = 0.05

R0 calculated as: $\text{R0} = (\text{Vc} \times \text{R2} / \text{Z}) - \text{R1} - \text{R2}$

Concentration Formula

Based on MQ-3 datasheet power function: log10(ppm) = (log10(Rs/R0) - 0.62) / -0.66 mg/L = ppm × 0.00188

Signal Processing

• 20 samples per measurement (5ms interval)
• Ring buffer of 20 measurements for voltage averaging
• Noise filter: values < 0.05V discarded
• EMA smoothing for mg/L: α = 0.15
• Dead zone: ±1% around Z or < 0.01V difference

Intoxication Levels

Level	mg/L	Alert
Sober (S)	< 0.16	None
Light (L)	0.16 - 0.50	1 vibration
Medium (M)	0.50 - 1.00	2 vibrations
Heavy (H)	1.00 - 2.00	3 vibrations
Critical (C)	> 2.00	5 vibrations

Building from Source

git clone https://github.com/serjantlk/MQ-3-Alcometer.git
cd MQ-3-Alcometer
ufbt